The Amino Acid Sequence of Ribonuclease N₁, a Guanine-Specific Ribonuclease from the Fungus Neurospora crassa

Abstract

The complete amino acid sequence of ribonuclease N₁ (RNase N₁), a guanine-specific ribonuclease from a fungus, Neurospora crassa, was determined by conventional protein sequencing, using peptide fragments obtained by tryptic digestion of cyanogen bromide-treated RNase N₁ and by Staphylococcus aureus V8 protease digestion of heat-denatured RNase N₁. The results showed that the protein is composed of a single polypeptide chain of 104 amino acid residues cross-linked by two disulfide bonds and has a molecular weight of 11, 174:
ACMYICGSVCYSSSSISAALNKGYSYYEDGATAGSSSYPHRYNNYEGFDFPTAKPWYE
FPILSSGRVYTGGSPGADRVIFDSHGNLDMLITHNGASGNNFVACN
(Disulfide bonds: C2-C10, C6-C103)
The amino acid sequence was homologous with those of RNase T₁ (65% identity) and related microbial RNases.